We describe a case of a large sinus of Valsalva aneurysm originating from the noncoronary sinus. The aneurysm compressed the roof of the left atrium rendering the annulus and the anterior leaflet of the mitral valve severely distorted and, as a result, incompetent. The neck of the aneurysm was closed with a patch from the side of the aortic sinus, but we had to replace the mitral valve as the distorted structure did not resume its original shape even though we opened the aneurysm and debrided all thrombotic material inside the aneurysm.